One of the most common problems encountered in an industrial environment is that of determining the reactive compatiblity of two or more substances when they are mixed. The necessity of determining such compatibility arises when waste materials are mixed for or during disposal, during absorption of accidentally spilled materials, or in the formulation of a chemical product. The problems inherent in mixing substances of these kinds have been recognized heretofore and a number of techniques proposed for their solutions.
In one of the prior art techniques differential scanning calorimetry (DSC) or differential thermal analysis (DTA) is used to detect potentially hazardous interactions in a mixture of a number of individual components. One of the problems with this procedure is that a reaction may occur as a result of mixing which cannot be detected using either of the DSC or DTA techniques. For example, the DSC curves of solutions of aqueous NaOH and HCl appear unchanged from the resulting NaCl solution formed upon their mixing, yet the reaction resulting from the mixing can produce enough heat to boil the resultant water in those instances in which concentrations of the reactants are sufficiently great. Typically, this problem has been circumvented by establishing estimates of heats of mixing by the use of a Dewar flask fitted with a thermocouple or thermometer. Volumes used in such a test typically range from 10 mL up to 150 mL.
Another procedure for use in assessing potential hazards resulting from binary mixtures is an adiabatic mixing test. This test involves a three-step method including the measurement of the adibatic temperature rise of a 1:1 molar mixture of the materials in an open Dewar flask. A measurement of the pressure change upon mixing of such materials observed to react below 46.degree. C. also was made in a sealed Dewar flask or instrumented Parr bomb (for the most reactive materials). Finally, those materials observed not to react upon initial mixing were subjected to DTA.
The adiabatic mixing test has been attractive because it involves a total approach of determination of the reaction upon mixing, as well as the higher temperature thermal stabilities. In addition, pressure measurements are of considerable significance in the evaluation of the overall potential hazard. It has been observed, however, that the experimental temperature rises increase as the volumes used in the tests increase. This is due to the relatively large changes in heat losses of the reaction vessel system as the volumes of the materials are increased. Although the observed temperature rises in small-scale tests approach those of a large-scale process as the volumes increase, safety risks increase when larger quantities of materials are used in the tests for obtaining more accurate data relating to temperature rises.
Another prior art technique utilizes an accelerating rate calorimeter (ARC). In this technique one of the materials is present in the bomb and another material is introduced to the bomb via a syringe having a long, small gauge dispensing needle. The temperature in the ARC then is increased to detect any potentially hazardous reactions. Although this technique is sound, it is lengthy and expensive to perform. Typical ARC tests require as long as eight to ten hours to complete. Further, serious errors can arise from the temperature mismatch of the added material. For example, 2 mL of aqueous material at 23.degree. C. added to the bomb at 30.degree. C. yielded a 14 caloric decrease. This endothermic heat can partially mask exothermic reaction.
An object of the present invention is to provide an apparatus and method for assessing the hazard of mixing materials and which overcome the problems associated with the prior art methods and apparatus.